Iran's military unveiled a new version of its homebuilt Qaher F313 fighter jet last weekend, but a drive down the runway revealed it's far from ready for flight.

A mysterious airplane that the Iranian government claims is its first stealth fighter prototype has reappeared after a more than three-year absence.

The Qaher F313 that first appeared on Iranian state media in February 2013 was clearly not a flyable warplane. It was, instead, a mock-up—one that either represented a functional future jet... or was purely for show. A propaganda prop.

The version of the Qaher F313 that reappeared on April 15, 2017 is also fake, albeit less obviously. Unlike the 2013 model, the 2017 model can move under its own power.

But it's still just a mock-up. We can reasonably assert this because the engineers who built the 2017 fake, following standard procedure, dutifully stenciled the plane's standard tire pressure on the fuselage. And that pressure is way too low for a real jet.

In other words, Iran is apparently no closer to developing a working stealth fighter than it was three years ago.

The Qaher F313 inspired great excitement when it debuted in official photos in 2013. Long embargoed by major world powers—and thus most big aerospace companies—Iran has had to develop its own aviation industry.

It's met with some success. Iran has managed to maintain and upgrade its four- and five-decade-old F-4 and F-14 fighters, for instance.

But new-start warplanes—especially sophisticated fighters—had, up to 2013, proved too ambitious for Tehran's aerospace industry. So observers were skeptical of the F313. Moreover, the demonstration model had features that quite clearly marked it as a non-flying mock-up. It lacked engine nozzles. Its cockpit was too small to fit a normal-size pilot. Official statements specified that the F313 could carry two 2,000-pound bombs plus six air-to-air missiles—a huge load for such a small fighter.

War Is Boring reporter Steve Weintz proved fairly definitively that eight weapons simply would not fit on the F313. Weintz built a scale model of the F313. He managed to fit the missiles under the wings and one bomb under the fuselage. The only way to squeeze in a second bomb was to mount it on top of the F313's fuselage, behind the pilot in his impossibly tiny cockpit. Carrying a gravity bomb on top of your plane leads to obvious complications. To drop the bomb, you'd have to roll upside down.

The 2017 version of the F313 is much more convincing. The 2013 model apparently never moved under its own power—probably because it entirely lacked an engine of any kind.

The 2017 model, by contrast, has appeared in official videos slowly taxiing on an airfield tarmac. Not flying, mind you—just taxiing. The question was whether the new F313 had full-fledged aeroengines installed or just some small motor driving, say, the nose wheels.

Most likely it's the latter. Military analyst Galen Wright was the first to notice and post on Twitter that whoever built the 2017 edition of the purported stealth fighter stenciled the plane's tire pressure—50 pounds per square inch—on the side of the plane above the front landing gear.

Fifty PSI is way too little for a real warplane. Wright dug up a Pentagon document stating the standard tire pressure for the F-4 and F-15 fighters, among others—265 and 305 PSI, respectively, for roughly the same area of tire rubber. If the F313 can safely roll on tires inflated to just 50 PSI, it means it probably weighs no more than a fifth of what an F-4 does per unit of volume.

It is, in other words, mostly hollow. It must have a small motor of some sort to allow it to taxi. But it probably lacks aeroengines—and certainly can't fly. Unless you drive it off a cliff.